Tetrachromacy: a new colour vision phenotype?

Host:  Professor Alex Wade

About 12% of women are carriers of anomalous trichromacy caused by an X-linked red/green hybrid gene that encodes a cone photopigment with a spectral sensitivity somewhere between those of the normal M and L cone photopigments.  Random X-chromosome inactivation ensures that the retinal mosaic of such a carrier will contain four rather than three types of cone and people have speculated whether individuals with such four-cone retinae could enjoy four-dimensional colour vision.

We have recently been able to lend strong support for this hypothesis (Jordan, Deeb, Bosten & Mollon, 2010), but overall our results suggest that tetrachromacy is not afforded automatically to those with four types of retinal cone.

I will describe psychophysical tests and molecular analyses that have led to our conclusion and will speculate about the implications of tetrachromatic colour vision.